The present disclosure relates to an optical scanning device including scanning lenses for imaging light beams on surfaces to be scanned and an image forming apparatus using this.
For example, a general optical scanning device used in a laser printer, a copier or the like includes a light source for emitting a laser light beam, a polygon mirror for deflecting the laser light beam to scan the surface to be scanned with the laser light beam and a scanning lens for imaging the deflected laser light beam on a circumferential surface (surface to be scanned) of a photoconductive drum. In a color printer, photoconductive drums are provided for four colors of cyan (C), magenta (M), yellow (Y) and black (Bk) and each circumferential surface is scanned with a laser light beam modulated by image data of each color.
The optical scanning device is in a mode to be individually arranged for the photoconductive drum of each color or in a mode to be arranged for two colors or four colors by sharing a housing, a light source unit and optical components as widely used particularly in small-size printers. In the mode in which one optical scanning device is used for a plurality of colors, a polygon mirror is shared. In a two-color sharing type, two laser light beams are caused to be incident on the polygon mirror in different directions and the respective laser light beams are deflected by different mirror surfaces and imaged on the circumferential surfaces of corresponding photoconductive drums. In this mode, scanning directions of the laser light beams on one and the other drum circumferential surfaces are opposite (hereinafter, this mode is called an “opposite scanning method” in this specification).
Since the photoconductive drum rotates about an axis during one line scanning in a main scanning direction, a scanning line is inclined in a sub scanning direction. In the opposite scanning method, the inclination of the scanning line on one drum circumferential surface is opposite to that on the other drum circumferential surface. This causes a color shift in the sub scanning direction.